REAL ESTATE SECURITIES - Securities by Remaining Maturity (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	$ 618,227		$ 612,752
1-5 years	1,509,868		1,260,381
5-10 years	470,388		533,604
After 10 years	391		480
Fair value of real estate securities	2,598,874		2,407,217
Other than temporary impairments included in consolidated statements of income	(600)	$ (500)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	618,223		610,526
1-5 years	1,147,927		891,752
5-10 years	426,004		489,228
After 10 years	0		0
Fair value of real estate securities	2,192,154		1,991,506
CMBS interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		0
1-5 years	340,127		344,423
5-10 years	0		0
After 10 years	0		0
Fair value of real estate securities	340,127		344,423
GNMA interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	4		6
1-5 years	14,953		17,159
5-10 years	8,390		8,549
After 10 years	391		480
Fair value of real estate securities	23,738		26,194
GN construction securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year			0
1-5 years			386
5-10 years			28,253
After 10 years			0
Fair value of real estate securities			28,639
GN permanent securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		2,220
1-5 years	6,861		6,661
5-10 years	35,994		7,574
After 10 years	0		0
Fair value of real estate securities	$ 42,855		$ 16,455

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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